The present invention relates to a bead wire for tires, a rubber-coated bead wire for tires and a tire using the rubber-coated bead wires, and more particularly to a bead wire for tires which is plated with a metal mixture having a specific weight ratio in a specific amount, a rubber-coated bead wire for tires which is obtained by coating the specifically plated bead wire as mentioned above with a specific rubber composition and a tire prepared by using the rubber-coated bead wires as mentioned above.
In general, as to bead wires for tires, in order to improve the adhesion between a bead wire and the rubber layer formed on the bead wire, and particularly, when using the bead wires in a tire, to improve the deterioration of the adhesion resulting from the stress and heat caused by running the tire, the bead wire for tires is Cu/Sn-plated, then the plated bead wire is combined with a rubber composition which is coated on the plated bead wire (hereinafter referred to as "bead-coating rubber composition), and the obtained rubber-coated bead wire is used as bead cores in a tire.
The adhesion reaction between the bead wire and the rubber layer occurs during a vulcanization step, which is one step of the tire preparation steps. It is said that the adhesion reaction is caused between the bead wire and the rubber layer by the vulcanization to form a reaction layer. In order to obtain an excellent adhesion, it is necessary to obtain a reaction layer wherein the bead wire reacts with the rubber layer to form excellent adhesion.
Observing the rubber layer on the bead wire, as to the deterioration of the adhesion of tires in practical use, there are some tires wherein the peeling is caused in the reaction layer, which sometimes exerts a bad influence on the life of tires. When the bead wire does not strongly react with the rubber layer (the reaction layer does not have the excellent adhesion), the adhesion between the bead wire and the rubber layer is lowered by the stress and heat generated during the running of the tires. In some cases, the rubber layer is peeled off from the bead wire, and in other cases the bead wires protrude from the tire (such a damage of the bead portions is referred to as "wild wire"). Since the occurence of the above-mentioned disadvantages greatly depends on the stress and heat applied to the bead portions, these disadvantages are easily caused in tires used under conditions of heavy load and high speed, such as tires for airplanes which must bear a heavier load than loads applying to tires used in other categories and must withstand high speeds, such as not less than 300 km/hour.
In order to improve the disadvantages mentioned above, there has been known a method wherein triazine thiols are used as a crosslinking auxiliary for adhesion reaction between the rubber layer and the bead wire. When applying the method to tires used under the conditions of heavy load and high speed, for instance tires for airplanes, however, the adhesion is unsatisfactory and the cost becomes high.
An object of the present invention is to provide a bead wire for tires having an excellent adhesion.
A further object of the present invention is to provide a rubber-coated bead wire for tires having an excellent adhesion between the bead wire and the rubber layer.
A still further object of the present invention is to provide a tire improving the disadvantages as mentioned above.
These and other objects of the present invention will become apparent from the description hereinafter.